THE PILOT OF AN AIRPLANE INVOLVED IN A BANNER TOW OPERATION REPORTED THAT HE HAD COMPLETED A NORMAL TRAFFIC PATTERN AND APPROACH TO RUNWAY 30 TO PICK UP A BANNER. HE STATED THAT HE DID A ROUTINE PICK UP FOLLOWED BY A CLIMB. DURING THE INITIAL CLIMB, THE PILOT STATED THAT HIS ANGLE OF ATTACK WAS STEEP AND THE AIRPLANE STALLED. HE STATED THAT HE LOWERED THE AIRPLANE'S NOSE AND THAT THE ENGINE WAS AT FULL POWER, BUT THE AIRPLANE IMPACTED THE RUNWAY. WITNESSES ON THE GROUND REPORTED THAT THE WEATHER WAS CLEAR WITH LITTLE OR NO WIND. ONE WITNESS STATED THAT DURING THE INITIAL CLIMB, THE AIRPLANE BEGAN TO FLUTTER BEFORE FALLING TO THE GROUND AND IMPACTING THE RUNWAY. EXAMINATION OF THE ENGINE BY THE FAA DID NOT DISCLOSE EVIDENCE OF MECHANICAL MALFUNCTION. THE INVESTIGATION ALSO REVEALED THAT THE PILOT HAD RECEIVED HIS ENDORSEMENT FOR BANNER TOWING SIX DAYS PRIOR TO THE ACCIDENT.